Static
electrification (SE) in transformers is an interfacial phenomenon, which involves
oil, paper and transformer board. Its physical mechanism involves a source of
charge and region of excessive charge accumulation.

Extensive investigations
about this phenomena have been made during recent years. 25 When oil is
forced through the tank and coolers, it acquires an electrostatic charge, i.e.
it contains an equal number of positive and negative ions.

When the oil
passes the paper and solid insulation in the windings, the insulation becomes
negatively charged and the oil positively charged with the charge separation
occurring at the oil-insulated interface (Fig. 6.16).

The earliest
reports on this phenomenon were in the 1970s from Japan, where number of h.v.
large transformer failures occurred. And later quite a few SE-related incidents
were also reported in the USA and other countries.

It is
believed that transformers of large rating (e.g. >100MVA) are most likely
affected by SE because they possess greater amounts of insulation and require
larger oil flow volumes than transformers of smaller ratings.

As different oils have different electrostatic
charging tendencies (ECT), oil additives might be a way to reduce oil ECT. As
an alternative to the additive, used oil can be regenerated because new oil exhibits
a lower ECT than aged oil.

On the other
hand, operation practices are also of great importance. SE incidents can be
caused by poor operating practices such as increasing forced oil cooling
capacity beyond manufacturer’s recommendations, or having more forced oil
cooling in operation than the load on the transformer justifies.

DISCLAIMER

Some of the links, content directing to links, videos, and other references are not owned and is not stored on the site. If you feel that we need to remove any of those aforementioned elements, feel free to inform the administrator of the site.